2seminar

programming

Obfuscated C

Basic moments

#include <stdio.h>
int x; // global variables here
 
int main() 
{
	int a; // local func variable
	a = 4; // assign value
	int b = 5; // or just init
	printf("Hello world!\n"); // print f - format
	printf("I like %d %d\n", x, y) // %d for int
	return 0;
}

comments

/* */ - multistring
// - single string

"aboba" - string, ended by ‘\0’
'C' - char

scape - последовательности

• \n - enter
• \t - tab

Basic types

long <=> long int

• char (may be signed) - 1 byte
• int (signed/unsigned) - 4 bytes
• short - 2 bytes
• long - 4/8 bytes
• long long (after ) - 8 bytes

---

• float - 4 bytes
• double (sec precision) 8 bytes
• long double - 10 bytes

---

• bool (added in C23)

---

• string

Constants

const int x = 4; - declaring unvariable variable
#define x 5 - declaring using preprocessor (pastes like macros and doesn’t use memory)

Operators

Sizeof

• sizeof(<type>) or sizeof(<object>) - возвращает количество выведенных символов

Scanf

• Scanf("%i %ld", &m, &n) - возвращает количество считанных переменных (-1 при ctrl+d как конец ввода/файла)
• завершается при расхождении ожидаемого и фактического ввода

Printf

Getchar

int getchar() - returns only int because it have -1 for End of FIle
int ch; ch = getchar()

Putchar

int putchar(<char>) - writes char

Strings

string - array of char ended by ‘\0’

0	1	2	3	4	5
H	e	l	l	o	\0

Translational specifiers

• %d - int
• %f
• %lf - float
  • %.2lf - 2 signs after dot
  • %6.2lf - 6 signs for all, 2 after dot
• %dd - double

specifiers	act
%d	int
%g or %e	sintific format

Arrays

int arr[LEN];
int arr[5] = {1, 2, 3, 4, 5}; - how does it work with 6 or 2 values?
arr[0] = 5
arr[4] - take last int in case

Loops

while

while (<condition>)
{

}

do while

for

for (<expression1>; <expression2>; <expression3>)
{

}

• expression1 - execute ones before operation
• expression2 - condition checks before iteration
• expression3 - executes after iteration

increments

• x++ - postfix
• ++x - prefix

int a, x = 4;
a = x++ // a := x and x := x + 1
a = ++x // a := x + 1 and x := x + 1

Example

#define LEN 5
int i;
int arr[LEN];
 
// fill the array
for (i = 0; i<LEN; i++)
{
	arr[i] = i
	printf("")
}

Functions

void smartPrint(int i); // header/declaration
 
int main ()
{
	smartPrint(3);
	return 0;
}
 
void smartPrint(int i) // defenition
{
	printf("\*\*\*%d\*\*\*\n", i);
}
 

Include

// myProg.h
int fun1()
{
 
}
int fun2()
{
 
}

// myProg.c
#include <stdio.h> // system folders
#include "myProg.h" // relative path
 
int main()
{
	fun1();
	return 0;
}